Welding has become a hot topic as of late. After structural repair procedures, welding is one of the most improperly performed procedures in collision repair. This can be due to a wide range of issues within the repair facility. Sometimes the equipment is outdated, damaged or simply not even in the shop, other times technician skill and training is lacking. Most often, it tends to be a combination of the two.
Here we are going to discuss the different types of welding methods used for steel and aluminum and the equipment and certifications required. Welding has become a big topic, with the 2015 Ford F-150, which is primarily aluminum, driving discussions, and because of the introduction of some new advanced high-strength steels (AHSS). Many OEMs have had to redesign their tool and equipment requirements, along with their training programs, because of these new substrates, or entirely make a new repair training program. Most of the aluminum collision repair certification programs require specific structural repair equipment and tools, welding equipment and certification to be on their program.
MAG (Metal Active Gas) welding steel
Only inert gases or gas mixtures are used for the shielding gas when MIG (Metal Inert Gas) welding. Typical inert gases used for MIG welding are argon and helium. These gases are usually used for MIG welding of aluminum and other non-ferrous metals.
MAG welding uses active gas mixtures that have been developed primarily for welding steels. Typical shielding gases are mixtures of argon, carbon dioxide and oxygen. Generally in collision repair the gas mixture is 75 percet Ar/25 percent CO2; 70 percent Ar/30 percent CO2; or 65 percent Ar/35 percent CO2.
The composition of the shielding gas has a substantial effect on the stability of the arc, metal transfer and the amount of spatter. The shielding gas also affects the behavior of the weld pool, particularly its penetration and the mechanical properties of the welded joint. At one time MAG welding was the only way to weld panels together in the collision repair field. Once Squeeze Type Resistance Spot Welders (STRSW) were developed for the collision industry, MAG was still preferred. But due to the development of AHSS and the heat affect on the these metals, AHSS welding manufactures were forced to produce more advanced STRSW. Although STRSW is the preferred method, MAG welding is still allowed by many OEMs for outer panel replacement. MAG is even required in certain situations where the STRSW arms cannot reach both sides of the panel or for certain structural component replacement. Obviously, MAG is required for seam welding in sectioned areas.
STRSW
Squeeze Type Resistance Spot Welding is the preferred method for replacing outer panel structural components, as per most OEM replacement procedures. In some cases, the OEM requires STRSW for replacement of their components, providing the arms can reach both sides of the flange. Some manufactures will allow STRSW on flanges and in areas accessible by the arms. Since no one allows single-sided welding, most OEMs will allow MAG plug welds and some limited OEMs require rivets in areas where there is no backside access. STRSW has advanced to meet AHSS needs and ensure a small heat affect zone (HAZ). To be current with the types of steel materials utilized in late-model vehicles, most of the STRSW equipment you should own should have been purchased within the past five years. STRSW is not used for aluminum repair.
Weld bonding
Weld bonding is the process of applying structural bonding adhesive between the flanges, then resistance welding the panels together. Currently many OEMs use this process at the factory, but in the aftermarket field only Ford and Chyrsler (includes Dodge and Jeep) require the weld bonding process for replacement of their components. BMW uses weld bonding during the assembly of their vehicles, but for replacement of their weld-bonded panels they require rivet bonding. Modern STRSWs have specific settings for weld bonding. Just remember to shunt the first weld.
MIG brazing
MIG brazing (MIG-B) is welding performed with a gas metal arc welder, called gas metal arc welding/GMAW, with a silicone-bronze welding wire and 100 percent argon gas. MIG-B is gold in color, and is not a fusion weld. Sometimes referred to as silicone-bronze welding (SBW), MIG-B is not used in the assembly process — OEMs use the laser brazing process. Generally, you will find laser brazing on the roof to uni-side flanges and on some rear body panel flanges, but most OEMs require bonding for replacement of laser brazing. Toyota, Honda, VW and Mercedes-Benz are a few OEMs that have replacement procedures that require MIG brazing in the rocker and quarter panel sectioning areas. MIG brazing will likely become more of a required procedure as new advanced steels are introduced and require a lower HAZ.
MIG aluminum
Proper welding technique and cleanliness is crucial when welding aluminum. Techniques that are a little sloppy in steel welding will destroy an aluminum weld. You must weld like a machine, and porosity is a main area of concern when welding aluminum. When welding steel, you can use the push/forehand or pull/backhand technique, but with aluminum, you must use the push/forehand technique, as this will allow the weld site to be continuously protected by the shielding gas. Steel MAG welding uses a two-step trigger process, where you press the trigger (step 1) and the machine welds, and then you release the trigger (step 2) and the welding stops. When welding aluminum, a four-step trigger is the preferred method and sometimes it is required. A four-step trigger process is needed or required, due to a cold start at the beginning of the weld and the crater at the end of the weld. A four-step works as follows:
Step 1 — Hot Start: Depress the trigger and the welder starts at 150 percent of the weld current. For example, it you are set for 100 amps, the welder will increase the current to 150 amps. This Hot Start is generally only required for a second or two.
Step 2 — Welding Current: After one to two seconds release the trigger and the current drops back to the original setting. This step is where the majority of your welding is performed. Remember your finger is not on the trigger, the machine will be welding, however.
Step 3 — Crater Fill: As you get to the end of the weld, you will depress the trigger again and hold it depressed. The machine will slightly increase the gas and lower the current. This will do two things: clean the area and fill the crater that will form due to the amount of heat. This step is generally only need for two to three seconds.
Step 4 — Weld Stop: After two to three seconds, release the trigger and the weld current is cut off and the gas will stay on and flow for two to three seconds to cool the area.
Four-step trigger is a very important function when welding aluminum, and it does take some practice to get used to it, but once you do it will become easy. For the lower-end aluminum welders without four-step trigger, you will have to perform a tail-in/tail-out procedure. Tail-in/tail-out is where you begin your cold start on the panel and push into the joint to allow the heat to build up, and then at the end tail-out or off the joint and back on to the panel to allow the crater not to be on the joint. This procedure is not allowed by most of the OEMs. Another procedure to prevent cold starts/craters is to tack weld small pieces of the extra scrap aluminum to the flanges and start and finish you weld on those tabs. After your weld is complete, you can cut them off and dress the edges.
Aluminum welding is difficult but not impossible to learn and master; practice is paramount. Aluminum likes to be welded hot and fast, and many of the aluminum welds are long. Some weld flanges can be 300mm long (12 inches). Unlike steel, there is no skip welding allowed; it is start on one side, then weld to the end. Technique is extremely important. The better the machine the easier it will be for you to become a good welder. Technician skill, body position, hand position, gun angle, gun position and travel speed can all adversely affect the weld quality. Please keep in mind that the OEMs will require very specific machines and they can be very expensive. Aluminum MIG welders start on the low end around $3,500 up to $20,000 for the high-end welders.
Welding certification
This word “certification” has become a real catch phrase lately in the collision repair field. Each OEM with a collision repair program is using this term for their program and for their welding. Let’s look at some of the facts, and you can draw your own conclusions. Many of the OEM collision repair programs require some I-CAR training as a starting point. Some OEMs have decided to have I-CAR assist in a development of a specific vehicle-training program, while others have their own facility and training program. Most of the European OEMs require vehicle specific hands-on training classes at their own training facilities, while many of the US OEMs just require I-CAR classroom-type training. All the OEM programs have certain fees attached to them, along with some specific equipment purchases, facility appearance and general insurance coverage.
Many of the OEM programs require the repair facilities to obtain the I-CAR welding series to be accepted to their specific welding certification. A number of the US OEMs utilize I-CAR’s new welding certification program, which is where your technicians are tested at their facility with their equipment. All welding test samples are visually inspected and destructively tested and then measured for tear out with an I-CAR welding gauge, in a shop situation. The I-CAR test is a six to eight hour test and you know the results at the end of class. Recertification is required every five years.
Most of the European OEMs require the I-CAR aluminum-welding test and then they require their specific test. Most of the European OEMs have adopted the ISO 9606-2 Welding Certification for their aluminum programs. The ISO 9606-2 test is generally a 40-hour test taken over a one-week period at the OEM’s training facility. Mercedes-Benz requires 80 hours taken over two weeks for the initial test. After performing multiple different weld configurations on cast and plate aluminum, all in the overhead position, the samples are sent to a lab for testing. Some OEMs send only some samples to the lab, while other samples will be tested in-house by an ISO/AWS welding inspector. Recertification is every two years, except for Mercedes-Benz, which is every six months.
